Giant Mucinous Carcinoma Originating from the Appendix: A Case Report

Introduction: Appendiceal mucinous neoplasms can involve peritoneal pseudomyxoma or invasion of adjacent organs. This report describes a rare case in which a giant appendiceal mucinous carcinoma expansively developed in the retroperitoneum without perforating the abdominal cavity. Case Presentation: The patient was a 55-year-old woman with no relevant history who was admitted to our hospital after imaging examination revealed a retroperitoneal tumor. The clinical diagnosis was a retroperitoneal tumor involving the hedge mucin. The patient underwent right hemicolectomy and partial resection of the duodenum and right abdominal wall to ensure complete tumor resection. Histopathologic findings suggested that the tumor was a mucinous carcinoma arising from the appendix. The postoperative course was uneventful. Although adjuvant chemotherapy was performed for 6 months, peritoneal recurrence developed 7 years and 4 months postoperatively. Nine years have passed since the surgery, and the patient is alive and receiving chemotherapy. Conclusion: Detailed pathologic examinations revealed that the tumor originated from the appendix. The characteristics of mucinous carcinoma contributed to the extensive growth of the tumor.